1. Field of the Invention
The present invention relates to a drum washing machine. More particularly, it relates to a method and control apparatus of detecting eccentricity in a drum washing machine for detecting eccentricity of a tub, thereby to determine whether or not to perform a dewatering cycle.
2. Discussion of Related Art
As shown in FIG. 1, generally, a tub driving circuit in a washing machine includes a motor 3 actuated by driving power externally supplied thereto for transmitting rotary power to a tub, a speed sensing unit 4 for sensing rotational speed of the motor 3; an arithmetic and control unit 1 for receiving a signal from the speed sensing unit 4, selection signal generated at a key pad (not shown), and signals from various sensors (not shown) and producing various control signals; and a motor driving unit 2 for positively or reversely rotating the motor 3 according to each control signal of the arithmetic and control unit 1.
The following description concerns washing and hydro-extracting operation through the tub driving circuit having such configuration in the washing machine.
In the washing operation, the arithmetic and control unit 1 receives a rotational speed value of the motor 3 sensed by the speed sensing unit 4, a selection signal generated at the key pad (not shown), and signals from the various sensors (not shown) and produces various control signals.
Once the motor driving unit 2 is switched according to the control signal of the arithmetic and control unit 1 and current flowing in forward direction is applied to the motor, the motor 3 is actuated to rotate in the positive direction. The rotary power of the motor 3 is selectively transmitted to a pulsator (not shown) via a clutch (not shown). The pulsator is then interlocked and rotated, thereby to create mechanical, frictional effect between the pulsator and laundry in the tub.
The arithmetic and control unit 1 controls the rotation of the motor 3 continuously for a predetermined period of time to keep the motor 3 rotating at a predetermined control revolutions per minute (RPM) in the positive rotary direction. After the predetermined time elapses, the arithmetic and control unit 1 turns off the motor 3 for a specified time on reduce the speed of the motor 3 and interrupt it.
Once the motor 3 is brought to a standstill, the arithmetic and control unit o produces a control signal to switch the motor driving unit 2, thus applying reverse current to the motor 3. Driving direction of the motor 3 is then changed to the reverse rotary direction. Rotary power by the reverse rotation of the motor 3 is selectively transmitted to the pulsator (not shown) through the clutch (not shown). The pulsator is then interlocked and rotated, thereby to create mechanical, frictional effect between the pulsator and laundry in the tub.
The arithmetic and control unit 1 controls the rotation of the motor 3 continuously for a predetermined time to keep the motor 3 rotating at a predetermined control RPM in the reverse direction. After the predetermined time elapses, the arithmetic and control unit 1 turns off the motor 3 for a specified time to reduce the speed of the motor 3 and interrupt it.
This control over the positive/reverse rotation of the motor 3 by the arithmetic and control unit 1 is repeatedly performed until the termination of an overall laundry process. Alternative repetition of the positive and reverse rotation creates strong mechanical, frictional effect between the pulsator and the laundry in the tub. The laundry is cleaned due to the strong frictional effect.
The hydro-extracting operation is performed as follows.
According to a control signal of the arithmetic and control unit 1, the motor 3 reversely rotates at predetermined RPM (for example, 50 RPM), thereby to disentangle the laundry tangled during the washing operation to some degree. Subsequently, the motor 3 rotates in the positive direction at high speed according to a control signal of the arithmetic and control unit 1 and allows the tub to rotate at the high speed. The dewatering operation is implemented by way of continuously keeping the tub rotating at high speed.
Whether or not to commence the hydro-extracting operation depends on decision on eccentricity of the tub by the arithmetic and control unit 1. This is because, if the tub is eccentric more than a predetermined degree of eccentricity due to the laundry tending to one side, excessive shaking occurs resulting in big noise and breakage in various mechanical devices, such as a rotary shaft of the tub, when the tub rotates.
Accordingly, the driving circuit of the general washing machine has a function of decision on the eccentricity. The process of deciding the eccentricity of the tub will now be described with reference to the diagram shown in FIG. 2.
The arithmetic and control unit 1, based upon the rotary speed of the motor 3 sensed by the speed sensing unit 4, applies a control signal to the motor 3 to make the tub to reversely rotate at "II" RPM. When the tub reversely rotates at the "II" RPM, the laundry which has been twisted during the washing operation is untwisted. This is a laundry untwisting process. Subsequently, the RPM of the tub reaches point "III", the arithmetic and control unit 1 applies a control signal to the motor 3 to increase the rotational speed of the tub to "I" RPM in order to determine whether or not to commence the hydro-extracting operation. The "I" RPM is speed at which the laundry can be attached to the side wall of the tub and rotates along with the tub.
When the tub rotates at the speed of the "I" RPM, the arithmetic and control unit 1 performs constant speed control to maintain the rotational speed of the tub at the "I" RPM. If the arithmetic and control unit 1 applies constant driving voltage to the motor 3 transmitting the rotary power to the tub, the rotational speed of the tub may not be kept at the "I" RPM constantly and may be changeable according to the degree of the eccentricity of the laundry.
After a predetermined time elapses, when the rotational speed of the motor 3 is sensed to be at the point "IV" (the point where variation of the RPM is determined to be almost constant), the arithmetic and control unit 1 senses a current variation of the RPM through the speed sensing unit 4. On the basis of the variation of the RPM at this point, the arithmetic and control unit 1 performs the decision on the eccentricity of the tub, thereby to perform the hydro-extracting operation or laundry untwisting process according to the decision. Afterward, the arithmetic and control unit 1 newly performs the decision on the eccentricity.
Here, adequate time must be given between the points "III" and "IV" because, if the interposed time between the two points "III" and "IV" is not adequate, there may occur an error in the decision on the eccentricity. In the period between the two points "III" and "IV" before the variation of the RPM converges on the predetermined range, the vibration of the RPM is great, so there is possibility of determining that the eccentricity is severe even when the eccentricity of the tub is small.
The process of decision on the eccentricity of the tub is as follows.
As the degree of the eccentricity of the laundry becomes greater, a deviation between the rotational speed of the tub and the "I" RPM gets larger. If the deviation between the rotational speed of the tub and the "I" RPM greatly changes in an instant, a corresponding signal waveform appears as the form of pulses having a peak. In turn, the arithmetic and control unit 1 measures the number of pulses (the number of RPM values) deviating from the "I" RPM for a unit of time and measures the degree of eccentricity of the laundry in the tub based upon the number of the pulses.
After measuring the degree of eccentricity through the above procedure, the arithmetic and control unit 1 compares the measured degree of eccentricity with a predetermined reference degree of the eccentricity. If the measured degree of the eccentricity is less than the reference degree of eccentricity, the arithmetic and control unit 1 performs the hydro-extracting operation. Alternatively, if the measured degree of eccentricity exceeds the reference degree of eccentricity, the arithmetic and control unit 1 controls the RPM of the motor 3 so as to newly perform the laundry untwisting process.
Afterwards, the arithmetic and control unit 1 newly measures the degree of eccentricity according to the procedure illustrated above and performs the hydro-extracting operation or laundry untwisting process according to a measured result. When repeating the measure of the eccentricity, the arithmetic and control unit 1 counts the number of times of the measuring processes. If the measure of the eccentricity is repeatedly performed more than a predetermined number of times, the arithmetic and control unit 1 treats this state as an unbalance error, thereby to terminate all the operation of the washing machine.
In other words, if the measured degree of eccentricty exceeds the predetermined reference degree even though the arithmetic and control unit 1 repeatedly performs the laundry untwisting process to regulate the degree of eccentricity of the laundry in the tub, the arithmetic and control unit 1 determines that this level of the degree of eccentricity of the laundry cannot be regulated by the washing machine itself, thus interrupting all the operation of the washing machine.
However, the eccentricity detecting method in this conventional drum washing machine is to apply constant driving voltage to the motor and measure degree of eccentricity under the stableness of RPM. This conventional eccentricity detecting method in the general drum washing machine requires much time to make the motor be in a stable status. In addition, there may occur a situation where the degree of eccentricity is difficult to be measured according to the volume of the laundry, thus interrupting accurate measure of the degree of eccentricity. Therefore, the eccentricity detecting method of the conventional drum washing machine has a problem in that shaking and noise rapidly occurs when the hydro-extracting operation is commenced.
This is because the eccentricity detecting method of the conventional drum washing machine compares the measured degree of eccentricity with the reference degree of eccentricity without considering the volume of the laundry though the degree of eccentricity is influenced by the laundry volume. When the driving circuit of the washing machine rotates the tub containing much laundry therein at high speed, the laundry is uniformly distributed in the side wall of the tub resulting in a small degree of eccentricity. Alternatively, when rotating the tub containing small amount of laundry therein at high speed, the laundry is gravitated to a portion of the side wall resulting in significant eccentricity. In the eccentricity detecting method of the conventional drum washing machine, the degree of eccentricity is measured without considering the volume of the laundry, so the washing machine has serious possibility of performing wrong operation.
In the conventional eccentricity detecting method, the constant driving voltage is applied to the motor to rotate the tub at the predetermined speed ("I" RPM) and detects the number of pulses (the number of RPM values) deviating from the "I" RPM for the unit time, thereby to measure the degree of eccentricity based upon the detected number. Accordingly, the conventional eccentricity detecting method requires constant speed control for constantly keeping the tub rotating at predetermined speed.
However, according to the conventional art just applying constant driving voltage to the motor 3 for the constant speed control, does not result in the tub being kept at aimed speed, the "I" RPM. The reason is that, although the motor is controlled with the constant driving voltage, actual rotational speed of the tub is not continuously kept at the predetermined speed, "I" RPM and changes irregularly because of the volume of the laundry in the tub and its eccentricity.
After all, the degree of eccentricity measured according to the conventional method cannot be said accurate since it is measured under the state where the rotational speed of the tub is not constant.